U.S. patent application number 10/436349 was filed with the patent office on 2003-10-16 for chemical mix and delivery systems and methods thereof.
Invention is credited to Forshey, Randy, Johnson, Kenneth A..
Application Number | 20030192920 10/436349 |
Document ID | / |
Family ID | 29399714 |
Filed Date | 2003-10-16 |
United States Patent
Application |
20030192920 |
Kind Code |
A1 |
Forshey, Randy ; et
al. |
October 16, 2003 |
Chemical mix and delivery systems and methods thereof
Abstract
The present invention relates to chemical delivery systems and
methods for delivery of liquid chemicals. In one embodiment, the
present invention relates to systems having multi-reservoir load
cell assemblies for delivering chemicals used in the semiconductor
industry. In one embodiment, the present invention provides a
multi-reservoir load cell assembly, including a controller, a
buffer reservoir, a main reservoir, one or more load cells, coupled
to the assembly and to the controller, operable to weigh the liquid
in the reservoir(s), a plurality of supply lines, each supply line
having a valve and connecting one of the supply containers to the
main reservoir, and a gas and vacuum sources for withdrawing the
liquid from the assembly when demanded by the controller and for
refilling the assembly from the supply containers.
Inventors: |
Forshey, Randy; (Discovery
Bay, CA) ; Johnson, Kenneth A.; (Stockton,
CA) |
Correspondence
Address: |
Robert Moll
1173 St. Charles Court
Los Altos
CA
94024
US
|
Family ID: |
29399714 |
Appl. No.: |
10/436349 |
Filed: |
May 12, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10436349 |
May 12, 2003 |
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10141644 |
May 6, 2002 |
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10141644 |
May 6, 2002 |
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09968566 |
Sep 29, 2001 |
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09968566 |
Sep 29, 2001 |
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09870227 |
May 30, 2001 |
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6340098 |
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09870227 |
May 30, 2001 |
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09568926 |
May 11, 2000 |
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6269975 |
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09568926 |
May 11, 2000 |
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09224607 |
Dec 31, 1998 |
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6098843 |
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09224607 |
Dec 31, 1998 |
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09222003 |
Dec 30, 1998 |
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Current U.S.
Class: |
222/504 |
Current CPC
Class: |
C30B 25/14 20130101;
B01F 2101/2204 20220101; B01F 35/881 20220101; B01F 35/7543
20220101; B67D 7/74 20130101; B01F 2101/58 20220101; B67D 7/0272
20130101; B67D 7/0238 20130101; B67D 7/0283 20130101; B67D 7/08
20130101; B01F 35/75 20220101 |
Class at
Publication: |
222/504 |
International
Class: |
B67D 003/00 |
Claims
What is claimed:
1. A chemical delivery system, comprising: a main reservoir in
fluid communication with one or more inlet fill valves, an inlet
pressure valve, and a main reservoir outlet valve; a buffer
reservoir in fluid communication with a buffer reservoir inlet
valve and a buffer outlet valve; a line connecting the main
reservoir outlet valve to the buffer reservoir inlet valve; a load
cell for monitoring the weight of a chemical in the buffer
reservoir and generating analog signals that are converted to
digital signals indicative of the weight of the chemical in the
buffer reservoir; a proportional valve block including a buffer
control inlet valve and a buffer control outlet valve that adjusts
the pressure to the buffer reservoir; a programmable logic
controller receiving the digital signals and generating control
signals to the proportional valve block to achieve a desired
chemical flow rate.
2. The system of claim 1, further comprising a load cell for
monitoring the weight of the chemical in the main reservoir and
generating analog signals that are converted to digital signals
indicative of the weight of the chemical in the main reservoir.
3. The system of claim 2, wherein the one or more inlet fill valves
includes a gross fill valve and a fine fill valve, and wherein the
programmable logic controller sends a signal to open the gross fill
valve until the main reservoir has almost sufficient chemical, and
another signal to the chatter the fine fill valve until the main
reservoir has the precise amount of chemical required.
4. The system of claim 2, wherein the programmable logic controller
sends control signals to each of the one or more inlet fill valves
sequentially so as to admit chemicals sequentially into the main
reservoir so that the load cell of the main reservoir can weigh
each chemical accurately.
5. The system of claim 4, further comprising a mixer assembly
including a motor, and a shaft and an impeller associated with the
main reservoir, wherein the programmable logic controller sends
control signals to engage the motor, rotate the shaft and impeller
which stirs the chemicals admitted into the main reservoir.
6. The system of claim 4, further comprising a mixer assembly
including a motor, and a shaft and an impeller associated with the
buffer reservoir, wherein the programmable logic controller sends
control signals to engage the motor, rotate the shaft and impeller
which continues to stir the mixture from the main reservoir that is
admitted into the buffer reservoir.
7. The system of claim 1, further comprising a pinch valve in fluid
communication and downstream of the buffer outlet valve, wherein
the programmable logic controller sends control signals to the
fully open the pinch valve to allow full flow during a flush
sequence and then return to a more closed determined set point.
8. The system of claim 1, further comprising an inert gas supply
that is in communication with the main reservoir and the buffer
reservoir.
9. The system of claim 8, wherein the inert gas supply is passed
through an inert gas humidifier so that the gas is humidified with
the liquid in the inert gas humidifier.
10. The system of claim 8 or 9, wherein the chemical being
delivered from the system is a chemical mechanical polishing
formulation whose primary component is de-ionized water and the
inert gas is nitrogen.
11. A method of liquid chemical delivery at low flow rates in a
system comprising a multi-reservoir load cell assembly, including a
main reservoir, a buffer reservoir, each reservoir having at least
one load cell and a mixer, and a logic device, comprising:
isolating the main reservoir from the buffer reservoir; reducing
pressure in the main reservoir; adding liquid chemical components
sequentially into the main reservoir; weighing each liquid chemical
component by the multi-reservoir load cell assembly; mixing the
chemical components into a mixture; supplying the main reservoir
with an inert gas; transporting mixture from the main reservoir to
the buffer reservoir; and transporting the mixture from the buffer
reservoir through a pinch valve.
Description
[0001] This application is a continuation of U.S. application No.
10/141,644, filed on May 6, 2002, which is a continuation-in-part
of U.S. application Ser. No. 09/968,566, filed on Sep. 29, 2001,
which is a continuation of U.S. application Ser. No. 09/870,227,
filed on May 30, 2001, now U.S. Pat. No. 6,340,098, which is a
continuation of U.S. application Ser. No. 09/568,926, filed on Feb.
13, 2001, now U.S. Pat. No. 6,269,975, which is a continuing
prosecution application of U.S. application Ser. No. 09/568,926,
filed on May 10, 2000, now abandoned, which is a divisional of U.S.
application Ser. No. 09/224,607, filed on Dec. 31, 1998, now U.S.
Pat. No. 6,098,843, which is a continuation of U.S. application
Ser. No. 09/222,003, filed on Dec. 30, 1998, now abandoned. This
application incorporates by reference each application and each
patent listed above.
BACKGROUND
[0002] The present invention relates generally to systems and
methods for mixing and/or delivering of liquid chemical(s), and
more particularly, to systems and methods for mixing and delivering
liquid chemicals in precise amounts using logic devices and
multi-reservoir load cell assemblies.
[0003] The present invention has many applications, but may be
explained by considering the problem of how to deliver photoresist
to silicon wafers for exposure of the photoresist in the process of
photolithography. To form the precise images required, the
photoresist must be delivered in precise amounts on demand, be free
of bubbles, and be of precise uniform thickness on the usable part
of the wafer. The conventional systems have problems as discussed
below.
[0004] As shown in FIG. 1, a representative conventional
photoresist delivery system includes supply containers 100, 102,
typically bottles, which supply photoresist to a single-reservoir
104 by line 117, which is connected to supply lines 106, 108
monitored by bubble sensors 110,112 and controlled by valves V1 and
V2. The bottom of the reservoir is connected to a photoresist
output line 114 to a track tool (not shown), which dispenses
photoresist on the wafer. The space above the photoresist in the
reservoir 104 is connected to a gas line 118 which, based on
position of a three-way valve V3, either supplies nitrogen gas to
the reservoir 104 from a nitrogen manifold line 126, regulated by
needle valve 1, or produces a vacuum in the reservoir 104. To sense
the level of the photoresist in the reservoir 104, the system
employs an array of capacitive sensors 122 arranged vertically on
the walls of the reservoir 104. A two-way valve V4, located between
the nitrogen gas manifold and the inlet of a vacuum ejector 124,
supplies or cuts off flow of nitrogen to the vacuum ejector
124.
[0005] The photoresist delivery system must be "on-line" at all
times so the track tool can dispense the photoresist as required.
Many of the photoresist delivery systems attempt to use the
reservoir to provide an on-line supply of photoresist to the track
tool, but the photoresist delivery system must still refill the
reservoir on a regular basis, which is dependent on timely
replacement of empty supply containers. Otherwise, the track tool
will still fail to deliver the photoresist when demanded.
[0006] During dispense mode, when the track tool withdraws
photoresist from the reservoir 104, the valve V3 permits the
nitrogen to flow from the nitrogen manifold to the reservoir 104 to
produce a nitrogen blanket over the photoresist to reduce
contamination and to prevent a vacuum from forming as the
photoresist level drops in the reservoir. Once the photoresist in
the reservoir 104 reaches a sufficiently low level the system
controller (not shown) initiates refill mode, where a set of
problems arise.
[0007] During refill mode, the valve V4 is activated so that
nitrogen flows from the manifold line 126 to the vacuum ejector
124, which produces a low pressure line 170 thereby producing a low
pressure space above the photoresist in the reservoir 104. The
bubble sensors 110,112 monitor for bubbles in the supply lines
106,108, presumed to develop when the supply containers 100, 102,
become empty. If, for example, the bubble sensor 110 detects a
bubble, the controller turns off the valve V1 to supply container
100 and the valve V2 opens to supply container 102 to continue
refilling the reservoir 104. However, bubbles in the supply line
106 may not mean supply container 100 is empty. Thus, not all of
the photoresist in supply container 100 may be used before the
system switches to the supply container 102 for photoresist. Thus,
although the conventional system is intended to allow multiple
supply containers to replenish the reservoir when needed, the
system may indicate that a supply container is empty and needs to
be replaced before necessary.
[0008] If the supply container 100 becomes empty and the operator
fails to replace it and the system continues to operate until the
supply container 102 also becomes empty, the reservoir 104 will
reach a critical low level condition. If this continues, bubbles
may be arise due to photoresist's high susceptibility to bubbles;
if a bubble, however minute, enters the photoresist delivered to
the wafer, an imperfect image may be formed in the photolithography
process.
[0009] Further, if the pump of the track tool, connected downstream
of the chemical output line 114, turns on when the reservoir is
refilling, the pump will experience negative pressure from the
vacuum in the single-reservoir pulling against the pump. Several
things can happen if this persists: the lack of photoresist
delivered to the track tool may send a false signal that the supply
containers are empty, the pump can fail to deliver photoresist to
its own internal chambers, lose its prime and ability to adequately
dispense photoresist, and the pump can even overheat and burn out.
The result of each scenario will be the track tool receives
insufficient or even no photoresist, known as a "missed shot,"
which impacts the yield of the track tool.
[0010] The present invention also may be explained by considering
the problems associated with mixing and delivering slurry for
chemical mechanical polishing (CMP). In semiconductor
manufacturing, a slurry distribution system (SDS) delivers CMP
slurry to the polisher. For example, Handbook of Semiconductor
Manufacturing Technology (2000), which is incorporated by
reference, describes delivery of CMP slurries to a polisher and
shows an arrangement for a SDS at page 431. In some applications,
the SDS needs to mix the components of the slurry in a mix tank.
During mixing and handling of the slurry, the SDS must not damage
the slurry by subjecting it to too much shear, which may cause
aggregation, or too little shear, which may cause settling. A pump
may transfer the slurry to a distribution tank when required by the
process tool. The SDS should handle a variety of chemistries
because a CMP slurry formulation is often tailored to each process.
The SDS should introduce precise of amounts of the slurry
components into a mix tank so that the slurry mixture is known. At
times, there also needs to be a precise flow rate to the process
tool and/or delivery at low flow rates. At low flow rates sometime
microbubbles form in the dispense lines, which prevents slurry
delivery. It would be desirable to clear lines without shut down of
the SDS. Of course, reliability for flawlessly daily manufacturing
and delivery of the slurry is also desired, as well as ease of
regular maintenance to avoid varying slurry composition that may
affect process results.
[0011] Flow meters are commonly used to control the flow rates of
chemicals. Flow meters are usually only accurate to within 2-3% of
the desired flow rate, and are also susceptible to changes due to
input pressure. Second, some chemicals will cause the flow meter to
plug up and allow no flow, i.e. slurries. Another method for
controlling flow is to use a "push" gas to pressurize a reservoir,
and then adjust the push gas pressure to adjust the flow rate. This
method also will not allow accurate flow rates, due to the
potential of the push gas pressure changing, and the flow rate
varying as the level within the reservoir changes.
[0012] The present invention addresses these problems as well as
avoids waste of chemicals, provides a friendly user interface
depicting the amount of chemicals remaining in the supply
containers, and reduces system capital and operating costs. If, for
example, the amount of chemical in the supply containers cannot be
seen, the present invention permits the interface to be provided at
a distance by conventional computer network capabilities and the
electronics provided.
SUMMARY OF THE INVENTION
[0013] The present invention relates to systems using controllers
or logic devices and multi-reservoir load cell assemblies for
precision mixing and/or delivery of liquid chemicals. It also
relates to methods of delivering liquid chemicals from supply
sources to processes such that the present invention accurately
accounts and adjusts for the dynamic supply and use of the liquid
chemical to meet process requirements. Finally, the present
invention provides multi-reservoir load cell assemblies for
monitoring, regulating, and analyzing the liquid supply available
to a process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 illustrates a chemical delivery system using a
single-reservoir and bubble sensors on the supply lines leading to
the single-reservoir.
[0015] FIG. 2A is a front cross-section of a first embodiment of
the multi-reservoir load cell assembly of the present
invention.
[0016] FIG. 2B is a top view of the first embodiment of the
multi-reservoir load cell assembly.
[0017] FIG. 3, a piping and instrument diagram, illustrates
embodiments of the chemical delivery system including the
multi-reservoir load cell assemblies of FIGS. 2A-2B or 4A-4B.
[0018] FIG. 4A is a front cross-section of a second embodiment of
the multi-reservoir load cell assembly.
[0019] FIG. 4B is a side cross-section of the second embodiment of
the multi-reservoir load cell assembly.
[0020] FIG. 5A is a front cross-section of a third and sixth
embodiment of the multi-reservoir load cell assembly.
[0021] FIG. 5B is a side cross-section of the third and sixth
embodiment of the multi-reservoir load cell assembly.
[0022] FIG. 6, a piping and instrument diagram, illustrates
embodiments of the chemical delivery system including the
multi-reservoir load cell assemblies of FIGS. 5A-5B or 11A-11B.
[0023] FIG. 7A is a front cross-section of a fourth embodiment of
the multi-reservoir load cell assembly.
[0024] FIG. 7B is a side cross-section of the fourth embodiment of
the multi-reservoir load cell assembly.
[0025] FIG. 8, a piping and instrument diagram, illustrates an
embodiment of the chemical delivery system including the
multi-reservoir load cell assembly of FIGS. 7A-7B.
[0026] FIG. 9A is a front cross-section of a fifth embodiment of
the multi-reservoir load cell assembly.
[0027] FIG. 9B is a side cross-section of the fifth embodiment of
the multi-reservoir load cell assembly.
[0028] FIG. 10, a piping and instrument diagram, illustrates an
embodiment of the chemical delivery system including the
multi-reservoir load cell assembly of FIGS. 9A-9B.
[0029] FIG. 11A is a front cross-section of a seventh embodiment of
the multi-reservoir load cell assembly.
[0030] FIG. 11B is a side cross-section of the seventh embodiment
of the multi-reservoir load cell assembly.
[0031] FIG. 12, a piping and instrument diagram, illustrates an
embodiment of the chemical mix and delivery system.
[0032] FIG. 13, a flow chart, illustrates a flow rate control
system using the diminishing weight of liquid in at least one of
the reservoirs.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] In the first embodiment, the present invention includes a
multi-reservoir load cell assembly 200 as shown in FIGS. 2A-2B. The
assembly 200 can be part of the system shown in FIG. 3, and can
replace the problematic single-reservoir 104 and bubble sensors
110, 112 of FIG. 1.
[0034] In this embodiment, the assembly 200, constructed of Teflon,
SST, polypropylene or any chemical compatible material, includes an
upper compartment 202, a main reservoir 206, and a buffer reservoir
208, all in an outer housing 212. The buffer reservoir 208 is
sealed from the main reservoir 206 by a separator 209, and an
o-ring seal 211 seals the perimeter of the separator 209 to the
outer housing 212. The separator 209 uses a center conical hole 250
that allows an internal sealing shaft 204 to form a liquid and
gas-tight seal with the separator 209. The separator 209 forms a
liquid and gas-tight seal to the pneumatic tube 215 with an o-ring
seal 210. The main reservoir 206 contains a middle sleeve 214 that
forms a rigid separation between the separator 209 and the
reservoir cap 205. O-ring 203 seals the perimeter of the reservoir
cap 205 seals against the internal surface of the outer housing
212. The reservoir cap 205 seals against the internal sealing shaft
204, the chemical input tube 217, and the pneumatic tubes 215 and
218 with a set of o-ring seals 207, 220, 222, and 224 (hidden, but
location shown in FIG. 2B), respectively. Mounted to the reservoir
cap 205 is a spacer 244, which also mounts to the pneumatic
cylinder 226. The reservoir cap 205 is held in position by the
upper sleeve 233 and the middle sleeve 214. The outer Teflon
reservoir top 201 is bolted to the outer housing 212 and forms a
mechanical hard stop for the upper sleeve 233 and the pneumatic
cylinder 226. Pneumatic airlines for the pneumatic cylinder 226
penetrate the outer Teflon reservoir top 201 through the clearance
hole 260.
[0035] It should be clear that the present invention is not limited
to the delivery of CMP slurries or photoresist on silicon wafers.
For example, although the invention shows advantages over the
conventional system in this environment, the systems of the present
invention can deliver other liquid chemicals for other types of
processes. Because the novelty of the present invention extends
beyond the nature of the chemical being delivered, the following
description refers to the delivery of chemicals to avoid a
misunderstanding regarding the scope of the invention.
[0036] As shown in FIG. 3, the multi-reservoir load cell assembly
200 shown in FIGS. 2A-2B is suspended on and weighed by a load cell
412, preferably such as a Scaime load cell model no. F60X10C610E
and a programmable logic controller (PLC) 330, preferably such as
the Mitsubishi FX2N, a computer, or another conventional logic
device determines the volume of the chemical in the assembly 200
from the load cell weight and the specific gravity of the chemical.
For brevity, we will refer to that logic device as a PLC. As
chemical from line 217 is drawn into the main reservoir 206, the
load cell 412 outputs a small mV analog signal 324 proportional to
the weight on the load cell 412. In one embodiment, an ATX-1000
signal amplifier 326 boosts the small signal 324 to the 4-20
millivolt range and sends it to an analog-to-digital converter 328,
such as the Mitsubishi FX2N4-AD, and the output digital signal 332
is sent to the PLC 330. The PLC 330 can be rapidly programmed by
conventional ladder logic. During withdrawal of the chemical, the
weight of the assembly 200 decreases until the software set point
of the PLC 330 is reached.
[0037] As further shown in FIG. 3, the PLC 330 may control valves
V1-V5 using 24 DC Volt solenoid actuated valves, and activate them
by an output card such as the Mitsubishi FX2N. Each solenoid valve,
when opened, allows pressurized gas from regulator 2 such as a
VeriFlow self-relieving regulator, to the pneumatically operated
valves V1-V5 to open or close the valves. The sequence of operation
of the first embodiment is programmed in the PLC 330 so the
components shown in FIGS. 2A-2B and 3 work as described below.
[0038] Once the chemical drops to a certain level, the PLC 330
triggers the system shown in FIG. 3 to begin an automatic refill
sequence using the multi-reservoir load cell assembly 200 of FIGS.
2A-2B as follows:
[0039] a) A blanket of preferably low pressure, e.g., one psi inert
gas is continuously supplied by the regulator 1, such as a Veriflow
self-relieving regulator, to the main reservoir 206 by the
pneumatic tube 218.
[0040] b) The pneumatic cylinder 226 lifts the internal sealing
shaft 204, thereby sealing the buffer reservoir 208 from the main
reservoir 206.
[0041] c) Once the buffer reservoir 208 is sealed, the main
reservoir 206 is evacuated to a vacuum of approximately 28 inches
of mercury. As shown in FIGS. 2A-2B, the pneumatic tube 218 from
the main reservoir 206 connects to the output side of a three-way
valve V4. Valve V4 is actuated so that the tube 218 communicates
with the line 316 connected to the vacuum ejector 324 as shown in
FIG. 3. The vacuum ejector 324 is powered by compressed gas, which
is directed to it by the two-way valve V5. Once valve V5 is on, it
allows compressed gas to pass through and the vacuum ejector 324
develops about 28 inches of mercury (vacuum) through the line 316
communicating with the main reservoir 206.
[0042] d) The vacuum is isolated from the buffer reservoir 208,
which has an inert gas slight blanket above it and continues to
supply chemical to the process or tool without exposing the
chemical being delivered to the tool to negative pressure or a
difference in pressure.
[0043] e) The vacuum generated in the main reservoir 206 creates a
low pressure chemical line that is connected to the valves V1 and
V2. Assuming that valve V2 opens, the low pressure line 217 causes
chemical from the supply container 102 to flow into the main
reservoir 206. During this period of time the main reservoir 206
refills with chemical until a determined full level is
achieved.
[0044] f) The full level is determined by use of the load cell 412
and weight calculations performed by the PLC 330. For example, one
preferred embodiment uses a buffer reservoir 208 with a volume
capacity of 439 cubic centimeters (cc) and a main reservoir 206
with a capacity of 695 cc. Using the specific gravity of the
chemical, the PLC 330 calculates the volume that the chemical
occupies. The PLC 330 then begins a refill sequence once the
chemical volume reaches or falls below 439 cc. The refill stops
once the chemical volume reaches 695 cc. This sequence allows
nearly all of the 439 cc of the chemical in the buffer reservoir
208 to be consumed while refilling the main reservoir 206 with the
695 cc of chemical and prevents overflow of the main reservoir 206
or complete evacuation of chemical from the buffer reservoir
208.
[0045] g) Once the main reservoir 206 has refilled, the valve V5 is
turned off, thereby stopping gas flow to and vacuum generation by
the vacuum ejector 324. The three-way valve V4 is then switched so
that the inert gas line 218 communicates with the main reservoir
206 and an inert gas blanket is again formed over the chemical in
the main reservoir 206 at the same pressure as the buffer reservoir
208, since both lines 218, 215 receive gas from the same inert gas
manifold 318 (see FIG. 3). Also, the valve V2 is closed which now
isolates the supply container 102 from the main reservoir 206.
[0046] After the main reservoir 206 is full of chemical with an
inert gas blanket above, the internal sealing shaft 204 is lowered
and allows chemical from the main reservoir 206 to flow into the
buffer reservoir 208. Eventually, the buffer reservoir 208
completely fills along with a majority of the main reservoir 206.
The pneumatic tube 215 connecting the buffer reservoir 208 fills
with chemical until the chemical in the tube 215 reaches the same
level as the main reservoir 206, because the pressures in both
reservoirs are identical. The internal sealing shaft 204 remains
open until it is determined, to once again, refill the main
reservoir 206.
[0047] Because the first embodiment uses load cells instead of
bubble sensors for determining the amount of chemical in the supply
containers, the present invention provides a number of very useful
features. One can accurately determine in real-time the chemical
remaining in the supply containers. If the supply containers are
full when connected to the system, the PLC can easily calculate the
chemical removed (and added to the multi-reservoir load cell
assembly) and how much chemical remains in the supply containers.
This information can be used to provide a graphical representation
of the remaining amount of chemical in the containers. A second
feature is that the PLC can determine precisely when a supply
container is completely empty by monitoring the weight gain within
the system. If the weight of the reservoir does not increase during
a refill sequence then the supply container is inferred to be
empty. This causes the valve for the supply container to be closed
and the next supply container to be brought on line. A related
third feature is the load cell technology provides the ability to
accurately forecast and identify the trends in chemical usage.
Since the exact amount of chemical is measured coming into the
reservoir the information can be easily electronically stored and
manipulated and transmitted.
[0048] A second embodiment of the multi-reservoir load cell
assembly 400 shown in FIGS. 4A-4B, includes a buffer reservoir 408,
fastened and sealed by the o-rings 411 to the bottom cap 410. The
output chemical flows through tube connection 401. Connected to the
buffer reservoir 408 are a pneumatic tube 415, a chemical valve
407, a load cell separator 413, and the load cell 412. The load
cell 412 is securely bolted to the buffer reservoir 408 and the
other side is securely bolted to a rigid member (not shown) not
part of the multi-reservoir load cell assembly 400. The outer
sleeve 404 slips around the buffer reservoir 408 and rests against
the bottom cap 410. The outer sleeve 404 is machined to allow the
load cell 412 to pass through it unencumbered. End 405 of the valve
407 connects to the main reservoir 406 and the other end 409
connects to buffer reservoir 408. The main reservoir 406 is
encapsulated and sealed, by o-rings in the upper cap 403. The upper
cap 403 incorporates a stepped edge along its periphery to secure
the outer sleeve 404 to it. Pneumatic line 418 and chemical input
line 417 are secured to the upper cap 403. The outer sleeve 404
provides the mechanical strength for the separate reservoirs 406
and 408.
[0049] The multi-reservoir load cell assembly shown in FIGS. 4A-4B,
and used in the system of FIG. 3, is similar to the first
embodiment with the following notable differences:
[0050] a) Valve 407 provides control of the fluid path between the
main reservoir 406 and the buffer reservoir 408.
[0051] b) The outer sleeve 404 provides the mechanical support to
form the rigid assembly that supports the main reservoir 406 as
well as the buffer reservoir 408.
[0052] A third embodiment of the multi-reservoir load cell assembly
shown in FIGS. 5A-5B, employs two reservoirs 506, 508 spaced apart
from each other but connected by a flexible fluid line 516. The
third embodiment uses many of the previous components shown in
FIGS. 4A-4B, except: (i) it does not use an outer sleeve 404; (ii)
the buffer reservoir 508 is not mechanically suspended from the
main reservoir 506; and (iii) the load cell spacer 513 and the load
cell 512 are fastened to the bottom of the main reservoir 506.
[0053] The third embodiment operates like the second embodiment
except the load cell 512 only measures the volume of chemical in
the main reservoir tank 506 as shown in FIGS. 5A-5B and 6. The
advantage of the third embodiment is the precise amount of chemical
brought into the main reservoir 506 is always known and the PLC
does not have to infer the amount of chemical that was removed from
the buffer reservoir 508 during a refill operation. The third
embodiment can be used in the system of FIG. 6 with the control
system (i.e., PLC, A/D, signal amplifier, etc.) of FIG. 3. Note, in
the application, the lead digit of the part numbers generally
indicates which drawing shows the details of the part, while the
trailing digits indicate that the part is like other parts with the
same trailing digits. Thus, the buffer reservoir 206 and the buffer
reservoir 306 are similar in function, and found in FIG. 2A and
FIG. 3A, respectively.
[0054] A fourth embodiment of the multi-reservoir load cell
assembly 700 shown in FIGS. 7A-7B, employs the same components as
the third embodiment, however, a second load cell 722 is attached
to the buffer reservoir 708. The assembly 700 is preferably used
with the system of FIG. 8 with the control system of FIG. 3 with
additional components for the second load cell.
[0055] The fourth embodiment of the multi-reservoir load cell
assembly 700 shown in FIGS. 7A-7B, operates much like the second
embodiment except that the load cell 712 only measures the chemical
in the main reservoir 706 and the load cell 722 only measures the
chemical in the buffer reservoir 708. The advantage here is the
buffer reservoir 708 is constantly monitored so if the downstream
process or tool suddenly consumes large amounts of chemical during
a refill cycle, the system can stop the refill cycle short to bring
chemical into the buffer reservoir 708 from the main reservoir 706
to prevent the complete evacuation of chemical from the buffer
reservoir 708.
[0056] A fifth embodiment of the multi-reservoir load cell assembly
900 shown in FIGS. 9A-9B uses the same components as the third
embodiment, except the load cell 912 is attached to the buffer
reservoir 908 instead of the main reservoir 906. The fifth
embodiment is preferably used in the system depicted in FIG. 10
with the control system (i.e., PLC, A/D, signal amplifier, etc.)
shown in FIG. 3.
[0057] Functionally, the fifth embodiment of the multi-reservoir
load cell assembly 900 operates the same as the second embodiment,
the only difference is the load cell 912 only weighs the chemical
in the buffer reservoir 908.
[0058] As the process or tool consumes the chemical, the weight of
the buffer reservoir 908 remains constant until the main reservoir
906 also becomes empty. Then the weight in the buffer reservoir 908
will start to decrease, indicating that the main reservoir 906
needs to be refilled. At this point the main reservoir 906 is
refilled for a calculated period of time. During this sequence the
buffer reservoir 908 decreases until the main reservoir 906 has
been refilled and the valve 907 has been reopened between the two
reservoirs 906, 908.
[0059] A sixth embodiment uses the same components of third
embodiment shown in FIGS. 5A-5B. The only notable difference is
that the inert gas blanket (see FIG. 6) of approximately one psi is
increased to approximately 80 psi (more or less depending on the
type of chemical). The increased inert gas pressure enables the
sixth embodiment to use pressure to dispense the chemical at a
constant output pressure, which remains unaffected even during the
refill cycle. This method would allow very precise non-pulsed
output flow of the chemical. This may be a highly critical feature
in an ultra high purity application that pumps the chemical through
a filter bank. Any pulsation of the chemical can cause particles to
be dislodged from the filter bank into the ultra-pure chemical
output flow.
[0060] A seventh embodiment uses the same components as the third
embodiment with additional components shown in FIGS. 11A-11B,
including a main reservoir 1106, a buffer reservoir 1108, a second
chemical input line 1119 added to the main reservoir 1106 through
the valve 1122, a valve 1123 added to the chemical input line 1117,
and a stir motor 1120 and an impeller assembly 1121.
[0061] Functionally, the seventh embodiment operates the same as
the third embodiment with the added capability of mixing two
chemicals in precise proportions before transferring the mixture to
the buffer reservoir 1108. The chemical can be drawn into the main
reservoir 1106 through open valve 1123 and the chemical input line
1117 and weighed by the load cell 1112. When the proper amount has
been drawn into the main reservoir 1106, the valve 1123 is closed
and the valve 1122 is opened to allow the second chemical to enter
the main reservoir 1106. When the proper amount has been drawn into
the main reservoir 1106, the valve 1122 is closed and the chemicals
are blended via the stir motor 1120 and impeller assembly 1121. The
stirring of the chemicals can be initiated at any time during the
above sequence. Once the mixing is complete, the valve 1107 opens
to allow the chemical to transfer to the buffer reservoir 1108,
which is also connected to gas line 1115. This is an ideal way to
mix time sensitive chemistries and maintain a constant, non-pulsed
output of the blended chemicals.
[0062] FIG. 12, a piping and instrument diagram, illustrates an
embodiment of a chemical mixing and delivery system. For clarity we
will discuss how the system can be used to mix components together
into CMP slurry, but the system can be used to mix other chemicals.
FIG. 12 contains many parts, so to avoid clutter we use
double-digit part numbers rather than four-digit as the leading and
trailing digit convention would require as discussed at page
13.
[0063] The system includes a main reservoir 69 with DI water lines
supplying DI water through a gross fill valve 41 and a flow control
valve 43, and a fine fill valve 42. In an embodiment, the gross
fill valve is a {fraction (3/8)}-inch valve, and the fine fill
valve is a {fraction (1/4)}-inch valve. As discussed in connection
with FIG. 3, the PLC may control valves using 24 DC Volt solenoid
actuated valves, and activate them by an output card such as the
Mitsubishi FX2N. Each solenoid valve, when opened, allows
pressurized gas from regulator such as a VeriFlow self-relieving
regulator, to the pneumatically operated to open or close the
valves. These actuators will be referred to in the specification,
but will not be shown in FIG. 12 to reduce clutter.
[0064] In an embodiment, the PLC sends a signal to such an actuator
to open the gross fill valve 41 permitting water to rapidly begin
to fill the main reservoir 69. When the main reservoir 69 contains
almost sufficient water, the PLC provides another signal to an
actuator to close the gross fill valve 41 and to intermittently
open and close the fine fill valve 42, so called "chatter" the
valve. This permits the system to add the precise balance of DI
water required for the mixture. Of course, this gross fill and fine
fill arrangement can be used for any component but is most useful
if there is a major amount of that component in the final mixture.
The flow control valve 43 is a manual or automatic controlled valve
that compensates for the different water pressures available at a
given facility.
[0065] The DI water recirculates through a bypass 40 then back to
the DI return. If the velocity of the water recirculating is kept
above some level such as seven feet/sec, it will reduce or
eliminate bacteria formation. The purpose of the DI water is to
dilute Chem A, which represents slurry. The slurry passes through a
fine fill valve 44 to the main reservoir 69, through a bypass 53
and recirculates to the Chem A return, which reduces the settling
of abrasives suspended in the Chem A.
[0066] Chemicals B-D represent other components used in small
amounts such as stabilizers, surfactants, and pad conditioners
supplied through fine fill valves 46-48 into the main reservoir 69.
The PLC sends control signals to admit Chem A through Chem D
sequentially so that the load cells 12 and 13 of the main reservoir
69 can weigh each component accurately. The two load cells shown in
FIG. 12 may permit higher accuracy than one load cell, but the
number of load cells is not essential to the invention. The PLC
also sends control signals to the engage the main mixer motor 20,
which rotates the shaft 24 and impeller 21, which stirs the
components into CMP slurry. Process requirements will define the
best time period and rpm for the impeller 21. The impeller 21 will
continuously stir certain CMP slurry formulations.
[0067] As shown at the top of FIG. 12, an inert gas supply provides
inert gas through a regulator, a safety pressure relief valve 33,
and a check valve 35 to an inert gas humidifier. For some CMP
slurries nitrogen is preferred, but other chemicals require other
gases. One of ordinary skill will know what inert gas is suitable
for a given CMP formulation. For brevity we will discuss the inert
gas as being nitrogen, which is bubbled through a tube in the DI
water to humidify the nitrogen. This reduces the caking of the CMP
slurry mixture inside the main and buffer reservoirs. The
humidified nitrogen is supplied through the main reservoir pressure
regulator 51, an inlet pressure valve 50, and to the main reservoir
69. The vent valve 49 is a safety valve, which is normally open
(NO) when not actuated. As known, the set of check valves 16, 35,
37, 39, 76, 86,and 99 prevent backflow on the associated lines.
[0068] The main reservoir 69 transfers the mixed CMP slurry to
buffer reservoir(s). In one embodiment, the main reservoir 69 holds
two liters so that it can effectively service each of two buffer
reservoirs 71, 92, holding one liter each. The transfer of the CMP
slurry passes through a main reservoir outlet valve 58, through a
line, then to a buffer reservoir inlet valve 60. Likewise, the main
reservoir 69 transfers the CMP slurry initially through a main
reservoir outlet valve 57, through a line, then to a buffer
reservoir inlet valve 97. The process tool determines when the
buffer reservoirs 71 and 92 deliver the CMP slurry through dispense
lines 1 and 2. Manual valves 84 and 85 are associated with the
dispense lines 1 and 2 lines for safety.
[0069] Buffer reservoirs 71 and 92 each include a proportional
valve block, which will be used by the PLC to control the pressure
in each buffer reservoir. The PLC sends control signals to the
proportional valve block to maintain the pressure in the buffer
reservoirs that is necessary to achieve a desired flow rate of CMP
slurry from the buffer reservoirs. For example, the pressure
transducer, PT in FIG. 12, reads the pressure in the buffer
reservoir 71 and sends a signal indicative of that pressure to the
PLC. Based on the measured pressure and the pressure set point, the
PLC will send signals to the proportional valve block to either
open a buffer control inlet valve 80 to increase the buffer
reservoir pressure 71 or open a buffer control outlet valve 81 to
decrease the buffer reservoir pressure 71. Likewise, the pressure
transducer of buffer reservoir 92 reads the pressure and sends
signals to the proportional valve block to maintain the pressure
necessary for a desired flow rate of CMP slurry from the buffer
reservoir 92. Based on the PLC signals, the proportional valve
block will either open a buffer control inlet valve 56 to increase
or open buffer control outlet valve 52 to decrease the pressure of
the buffer reservoir 92. The buffer reservoir 92 also includes an
optional buffer manifold 90, which can be used as a mounting
surface to connect multiple buffer outlet valves, but is not
required for a single buffer outlet valve 87 as illustrated. The
buffer reservoir 71 is shown with a buffer manifold 72, which is
also not required for a single buffer outlet valve 73.
[0070] A pinch valve is located downstream of the buffer outlet
valve 73, and another downstream of buffer outlet valve 87. FIG. 12
shows one suitable control arrangement for the pinch valve of
buffer reservoir 71, which can be used for other buffer reservoirs
such as the buffer reservoir 92. In this arrangement, the PLC
connects to an air actuator 78, which controls the flow rate of
clean dry air (CDA) passing through a pressure regulator 79.
Although not depicted in FIG. 12, it should be evident that the
same communication channels, clean dry air source, and CDA lines
can be used as one embodiment for the control of the pinch valve of
the buffer reservoir 92. The signal amplifier 77, the A/D
converter, and the load cells shown in FIG. 12 can be the same
parts and have the same operation described in the earlier
embodiments. The mixer motor 93 rotates shaft 94 and impeller 95 in
the buffer reservoir 92, and the mixer motor 71 rotates shaft 65
and impeller 66 in the buffer reservoir 71. The buffer reservoirs
71 and 92 include buffer reservoir vent valves 62 and 53, which are
normally open to release pressure when not in service as safety
features.
[0071] The parts described can be obtained from the following
vendors. Partek, A Division of Parker Corporation located in
Tucson, Ariz. can provide suitable gross fill valves, part no.
PV36346-01, fine fill valves, part no. PV106324-00, valve manifolds
70, 72, and 90, part no. CASY1449, and check valves part number
CV1666. Another suitable PLC is the Mitsubishi AG05-SEU3M. A
suitable proportional valve block is part no. PA237 manufactured
and/or sold by Proportion Aire, Inc. located in McCordsville, Ind.
A suitable inert gas humidifier part no. 43002SR01, and pinch
valve, part no. PV-SL-.25, are manufactured and/or sold by Asahi
America located in Malden, Mass.
[0072] In operation, the chemical mix and delivery system has
different modes. The initial mode is a fill or refill sequence
where the system adds and mixes together the components in the main
reservoir 69. In one embodiment, the fill or refill sequence can be
implemented as follows:
[0073] 1. The PLC sends control signals to open the DI line and
Chem A-D lines to supply components to the main reservoir 69.
Although not the only arrangement, it is preferred to admit these
chemical components sequentially to the main reservoir 69 so that
the load cells 12 and 13 directly indicate the weight of each
component in the final mixture.
[0074] 2. The PLC sends control signals to an actuator to shut off
the inlet pressure valve 50 which would otherwise admit nitrogen to
the main reservoir 69 and to open the normally open vent valve 49
so any residual gases can vent from the main reservoir 69.
[0075] 3. The PLC sends control signals to start the mixer motor
20. In one embodiment, the mixer motor 20 starts when the impeller
21 is covered with DI water or Chem A, but the time is process
dependent and not part of the invention. It could start before,
during, or after the time Chem A-D and DI water enter the main
reservoir 69.
[0076] 4. The PLC sends control signals to an actuator to open the
inlet pressure valve 50 to increase the nitrogen pressure to a
sufficient pressure, e.g., 20 psig, determined by the flow rate and
process requirements.
[0077] The PLC or logic device(s) will also send control signals to
prepare the inert gas humidifier for service as follows:
[0078] 1. The PLC sends control signals to an actuator to close the
DI drain valve 36, which is normally open, of the inert gas
humidifier.
[0079] 2. The PLC sends control signals to open the DI inlet valve
38 so that DI water begins to fill the inert gas humidifier.
[0080] 3. The HI sensor associated with the inert gas humidifier
will subsequently detect a high DI water level and send signals to
the PLC to send control signals to close the DI inlet valve 38.
Separately, the HI HI sensor functions to send an alarm signal if
the DI water fills beyond the operational level.
[0081] 4. The PLC sends control signals to an actuator to open the
valve 34, which admits nitrogen to bubble up through the DI water
to humidify the nitrogen that flows from the inert gas humidifier.
The valve 34 is either all the way open or all the way closed. It
is normally closed (NC) so that when the system is powered down,
that is, out of operation, valve 34 closes preventing introduction
of the inert gas, e.g., nitrogen into the inert gas humidifier.
[0082] 5. The inert gas humidifier feeds the nitrogen through the
lines up to the inlet pressure valve 50 and the buffer inlet
control valves 56 and 80. It should be noted that the pressure
supplied through the inlet pressure valve 50 is used to pressure
the CMP slurry out of the main reservoir 69 at the desired flow
rate.
[0083] The system transfers the CMP slurry mixed from the main
reservoir to the buffer reservoir as follows:
[0084] 1. The PLC sends a signal to open main reservoir dispense
valve 58 and to open buffer reservoir inlet valve 60.
[0085] 2. The PLC also sends signals to control the proportional
valve block to maintain the desired pressure in the buffer
reservoir(s), that is, the set point stored in the PLC. In one
embodiment, the set point pressure may be 5-12 psig when the
pressure of the main reservoir 69 is held at 20 psig. In one
example, a pressure transducer labeled PT in FIG. 12 provides the
pressure in the buffer reservoir 71 and the buffer control outlet
valve 81 opens if the pressure is too high or the buffer control
inlet valve 80 opens if the pressure is too low compared to the set
point for buffer reservoir 71.
[0086] 3. The mixer motor 93 or 64 of the buffer reservoir 92 or 71
stirs the components into a mixture. Again, the start time and time
period and rpm depend on the process.
[0087] In one embodiment, the process tool, for example, polisher,
triggers when the dispense valve outlet 87 and 73 of respectively
the buffer reservoir 92 and 71 open and close.
[0088] The load cells 91 and 96 of the buffer reservoir 92 send
signals to the PLC, which will be used to control the main
reservoir outlet valve 57 and the buffer inlet valve 97 for
transfer of CMP slurry between the main reservoir 69 and the buffer
reservoir 92. The buffer reservoir 71 operates by a similar
arrangement as shown in FIG. 12.
[0089] The load cells 12 and 13 associated with the main reservoir
69 will indicate when to add new components to make another batch
of CMP slurry. The main reservoir dispense valves 57 and 58 are
closed when the components are added to the main reservoir 69 so
that the load cells 12 and 13 accurately indicate the weight of
each component added to the main reservoir 69.
[0090] To clean and/or flush out the main reservoir 69, the PLC can
send control signals to close the main reservoir dispense valve 58,
open the gross fill valve 41 to admit DI water, open the main
reservoir dispense valve 57, close the buffer reservoir inlet valve
97, open the main reservoir drain valve 99 so that the DI water
passes from the main reservoir 69 bypassing the buffer reservoir
92. A similar sequence can be used with the buffer reservoir
71.
[0091] To clean and/or flush out the buffer reservoir 92, the DI
water can pass through opened main reservoir dispense valve 57,
opened buffer reservoir inlet valve 97, and closed main reservoir
outlet valve 89. The buffer reservoir 71 can be cleaned and/or
flushed by a similar arrangement as shown in FIG. 12.
[0092] In another embodiment, a fixed orifice pinch valve can be
employed in cases where ultra-low flow rates are unattainable due
to the properties of the mechanical components and the physical
attributes of the mediums being dispensed. This pinch valve uses a
flexible flow path that is compressed to a determined set point to
create a fixed orifice. This will allow the desired restriction in
the flow path necessary to increase or maintain a pressure for the
"push" to control very low flow rates. The pinch valve can be
actuated to open the flexible flow path to its maximum orifice to
allow full flow during a flush sequence and then return to the
desired determined set point. For example, a {fraction (1/4)}-inch
valve with a {fraction (1/4)}-inch orifice controls the push
pressure to the buffer reservoir to dispense the chemical. The
output valve for the fluid is also {fraction (1/4)}-inch. As the
flow rate decreases the pressure required to push also decreases.
In the case of ultra-low flow rate the inherent properties of the
valves controlling the push pressure limit the repeatability of the
precise volume of gas required to push. By installing the fixed
orifice pinch valve and increasing the restriction on the dispense
flow path, the push pressure can operate at higher levels resulting
in precise repeatable control of ultra-low flow rates.
[0093] A PLC and/or operator can adjust the pinch valve's minimum
and wide-open orifice size. The wide-open orifice setting can be
used to clear obstructions in dispense lines. Turning the pinch
valve wide-open is referred to as burping the line. This feature is
important for CMP slurries because microbubbles form during low
flow rates. The PLC can control the pinch valve so that pressure
builds up to permit ultra-low flow rates and burped after a process
cycle to clear any obstructions. The time period of the burp may be
short such as 0.5 seconds and performed after delivery of the CMP
slurry. A typical process only requires delivery of CMP slurry for
up to 1.5 minutes and microbubbles may not appear in some CMP
slurries for about 5 minutes so post-process burping may suffice.
If not, the dispense lines can be burped more frequently without
unduly affecting the flow rate over a given process cycle.
[0094] FIG. 13 illustrates the functional blocks of the PLC that
will be associated with one embodiment of the flow rate control
system, which uses the diminishing weight of CMP slurry or other
chemical mixture in at least one buffer reservoir. The load cells
constantly monitor the weight of the CMP slurry and generate analog
signals indicative of the weight of the CMP slurry in the buffer
reservoir. An A/D converter converts those analog signals into
digital format then sends them to the PLC. The PLC stores the
specific gravity of each component to calculate component volumes.
In parallel or serially with this activity, the user inputs through
a keyboard, keypad, or touch screen a desired volumetric flow rate
such as 200 ml/min. The PLC can convert the flow rate to rate per
second. Next, the PLC directs that the buffer inlet pressure valves
open to apply pressure to the buffer reservoir to produce the
desired flow. The PLC monitors the declining weight in a time
period and compares the current flow rate to the desired flow rate.
If the flow rate is too low, the PLC sends signals to the
proportional valve block to increase pressure, and if the flow rate
is too high, the PLC sends signals to the proportional valve block
to decrease the pressure. If the volumetric flow rate is within a
predetermined tolerance, the PLC send signals to the proportional
valve block that neither increase nor decrease the pressure to the
buffer reservoir.
[0095] In other words, a "push" gas is supplied to the buffer
reservoir by either a proportional control valve or valves and
pressure is monitored via a pressure transducer or transmitter. The
desired flow rate is entered, and a calculation is performed to
determine the required weight loss from the reservoir during the
course of a certain period of time. The PLC causes a signal to be
sent to the proportional valve to adjust the push gas pressure, to
adjust the weight loss within the reservoir to meet the flow rate
requirements. The weight loss can be monitored over the course of
time varying from 0.1 seconds to 60 seconds (or higher) depending
on the accuracy of the flow rate required. For example, a flow rate
of 180 milliliters per minute equals a flow rate of three
milliliters per second. The PLC monitors the weight change within
each buffer reservoir. If the weight loss is less than three
milliliters per second, the pressure is increased. If the weight
loss within the buffer reservoir is greater than three milliliters
per second, the pressure is decreased. To achieve greater accuracy,
the time frame can be shortened to the weight loss achieved during
the course of 12 second, or even as low as 0.1 second or lower. The
determining factor may be the resolution of the load cells
associated with the buffer reservoir. If the load cell is able to
resolve 0.1 gram, tighter controls can be implemented.
[0096] This embodiment requires no additional components to control
flow. Since no additional devices are used, the problems of
plugging are eliminated. Because the pressure to the reservoir is
controlled by the PLC, varying input pressures are accounted for
and proper adjustments are made to keep the flow at the desired
rate. The PLC can be used to determine the average pressure
utilized to maintain the proper flow rate. Once the level within
the buffer reservoir reaches a point to where it needs to be
refilled, the average pressure can be utilized to maintain the flow
rate while the buffer reservoir is refilling. The volume level is
also monitored real time, which alleviates any requirement for
additional components to detect level. The buffer reservoir will
dispense chemical as required to satisfy a request command
transmitted from the process tool. The volume level is replenished
when a low volume set point is triggered as the declining weight is
monitored. In like manner the volume being replenished is stopped
when a high set point is triggered as the increase in weight is
monitored.
[0097] The present invention provides at least the following
benefits. The output chemical can be maintained at a constant
pressure. A process tool never experiences a low-pressure chemical
line that could prevent a dispense sequence from occurring;
therefore the yield of the tool is increased. A multitude of
containers and sizes can be connected to the reservoir system as
chemical supply containers. If the fluid volume of the supply
containers is known before they are connected, the computer can
calculate very accurately the amount of chemical that has been
removed from the container and therefore present the information to
a display for a visual, real time indication of the remaining
amount of chemical. The graphical interface communicates to the
operator at a "glance" the condition of the supply containers. The
load cells can determine when the supply container is completely
empty since there will not be a continued weight increase during a
refill sequence. This indicates the supply container is empty and
that another container should be brought on line. In one
embodiment, data logging of chemical usage can be provided since
the chemical in the reservoir(s) is continuously and accurately
weighed by load cell(s) which give an input signal to the PLC or
other logic device which outputs real time, accurate information as
to the amount of chemical available in the reservoir. The load cell
is an inherently safe sensing device since failure is indicated by
an abnormally large reading or an immediate zero reading, both of
which cause the PLC or other logic device to trigger an alarm. The
invention can also prevent bubbles that occur during a supply
container switching operation from passing through to the output
chemical line, can provide constant, non-varying pressure dispense
with multiple supply containers, can refill itself by vacuum or by
pumping liquid to refill the reservoir or refill with different
chemicals at precise ratios and mix them before transferring the
mixture to the buffer reservoir, which may be important for time
dependent, very reactive chemistries.
[0098] The invention can provide precise flow control of fluids,
chemistries, and compound mixtures utilizing pressure reservoirs
fitted with valves, tubing, weight sensors (load cells), and a
control system. The invention can also monitor and control
volumetric level replenishment utilizing pressure reservoirs fitted
with valves, tubing, weight sensors, and a control system. The
invention can also replace the commonly used methodologies to
control precise flow, such as manually set throttle valves and flow
meters. The invention when fitted with the pinch valve can control
very precise low flow rate.
* * * * *